atrial fibrillation

noun

: very rapid uncoordinated contractions of the atria of the heart resulting in a lack of synchronism between heartbeat and pulse beat

If you're experiencing chest pain, palpitations, lightheadedness or shortness of breath, you could have atrial fibrillation (AF), a condition in which the heart's upper chambers (atria) "quiver."

—Abigail L. Cuffey, Woman's Day

—abbreviation AF

called also A-fib, auricular fibrillation